In mobile telephony communication systems, different types of antennas are used for transmission and reception of signals. An ordinary type of antenna is a so-called array antenna where antenna elements are arranged in adjacently arranged columns, one after the other.
When using array antennas, as for example used in TD-LTE (Time Division-Long Term Evolution), there is often a need to define beam ports with an associated beam pattern. These beam ports have different radiation characteristics than the individual, physical, ports of the array antenna. This is normally achieved by means of beam forming, which is commonly known, but in many cases this results in that power utilization becomes poor. The ultimate goal is to define ports with desired beam characteristics and with good power utilization.
Two beam ports may for example be used for CRS:s (cell specific reference signals), where the method predominantly used for the two CRS ports is a conventional beam forming where a signal is weighted and transmitted over multiple ports of the same polarization. This results in many cases in very poor power resource utilization.
WO 2011050866 and US 2012274514 describe dual polarized beamforming, where two beam ports may be obtained from a number of antenna ports of orthogonal polarizations. The beam ports have orthogonal polarizations for all angles.
However, now there is a desire to obtain primarily four beam ports, for example CRS ports, and for example implemented by means of dual polarized beamforming, from a four column dual polarized array antenna. The beam ports form two groups for which a port in one group has a polarization that is mutually orthogonal to the polarization of the ports in the other group. The two polarizations should be mutually orthogonal for all angles at the beam ports.